This invention relates to the field of artificial joint prostheses and, in particular, to an improved instrument for broaching a cavity in bone for receiving a prosthesis.
For implantation of prosthetic stems, such as hip stems, accurate preparation of the bone or intramedullary canal is important in order to guarantee good contact between the prosthesis stem and sleeve and the bone. The underlying concept behind precise preparation is that a precise bone envelope reduces the gaps between the stem and sleeve of the implant (i.e. prosthesis or prosthetic component) and the bone, thereby improving the initial and long-term bone ingrowth/fixation. The bone canal is presently prepared for implantation of a prosthetic stem by drilling and reaming a resected end of a bone, such as a femur, and then preparing an area adjacent the drilled hole to provide a seat for the prosthetic stem or a proximal sleeve coupled to the stem of a modular prosthetic system. A sleeve of modular prosthesis system is disclosed in U.S. Pat. No. 5,540,694, the disclosure of which is incorporated herein by this reference.
Preparation of the area adjacent the reamed intramedullary canal may be accomplished by broaching or by milling. Currently available broaches or rasps used for bone preparation have limitations. Some such broaches or rasps rely solely on the surgeon for guidance. Currently available broaches and rasps suffer from a tendency to be deflected by harder sections of bone so that they do not create a precise triangular cavity for receipt of the stem or sleeve of the prosthesis.
Thus, milling is currently the preferred method of bone preparation in many orthopaedic applications because it is a precise method of bone preparation. A limitation of milling systems today is that they are typically formed so that the drive shaft extends at an angle relative to the remainder of the frame from the end of the miller cutter machining the bone. A fairly large incision must be made to accommodate such milling assemblies. A typical incision for preparing a femur for a total prosthetic hip replacement using a standard triangle miller system is nine inches long. It is not uncommon for incisions as large as 12 inches to be used in a total hip replacement procedure. Efforts have been made to configure triangle miller systems to reduce the size of the incision required to accommodate a triangle miller during a prosthetic operation. However, to accommodate any miller, it is necessary to make an incision which may be undesirably large for cosmetic or other reasons.
In a hip replacement operation, initially, an incision large enough to expose the proximal end of the femur and to accommodate the instruments to be used in the operation is made in the upper thigh of the patient. Then, the neck of the femur is resected at the appropriate varus-valgus and anterior-posterior locations (typically determined using a template) with a resection instrument such as an oscillating saw. Then the femoral canal is opened up and the femoral cortex is reamed in preparation for receipt of the distal stem component of the prosthesis. Typically a stepped starter drill is utilized to generate an initial hole in the intramedullary canal. The stepped starter drill is positioned to open the trochanteric region to guard against varus positioning of the reamer and prosthesis. To further protect against varus positioning a box osteotome can be used to remove additional bone from the medial aspect of the greater trochanter.
Once the femoral canal has been appropriately opened, reaming begins utilizing a straight reamer. Distal reaming is done using a series of sequentially larger reamer diameters. The final straight reamer utilized should be ½ mm larger than the minor diameter of the selected femoral stem. The initial reamer is typically different from the rest in that it is an end cut reamer utilized to assist in canal finding, while the remaining reamers are blunt tipped side cutting reamers. The reamers are passed into the canal until a witness mark associated with the length of the stem component of the prosthesis to be utilized is adjacent the greater trochanter. The surgeon then works up progressively until cortical contact is made. Distal reaming is complete when the surgeon has reamed out to cortical bone in the shaft region.
The proximal or cone portion of the femoral metaphysis is then performed. Progressively larger cone reamers attached to an appropriately sized pilot stem are utilized to perform the cone portion of the femoral metaphysis. The cone reamer is advanced until an appropriate witness mark on the shaft is adjacent the greater trochanter. Successively larger cone reamers are used until cortical contact is achieved in the proximal femur.
Once cone reaming is completed calcar preparation is performed. Calcar preparation has been performed using triangular miller, broaches and reamers. When hand guided broaches or rasps or triangular millers are utilized for calcar prepartion, the initial incision must be fairly larger to accommodate these instruments. Following calcar preparation, a trial sleeve and trial implant are inserted into the proximal end of the femur. The trial sleeve is utilized to determine if anteversion or version must be changed in the prosthesis by performing trial reductions and adjusting the version and anteversion of the proximal trial component appropriately. Based on the trials, the final prosthesis components are selected assembled and inserted into the bone.
Since the oscillating saw used for neck resection and the straight reamers and conical reamers used for canal preparation are typically smaller than the instrument used for calcar preparation, the calcar preparation instrument often dictates the size of the incision required to perform the operation. When a patient undergoes total hip replacement (THR) it is common for the patient to stay in the hospital for one to two weeks. Rehabilitation therapy lasts months and many patients do not fully recover for years. Some patients never fully recover. This recovery process poses a substantial psychological and financial strain on THR patients. Many patients are in the latter years of their lives and this recovery period represents a significant portion of the remaining years. Current trends in joint replacement surgery suggest that smaller incision size can lead to faster recovery, improved quadriceps function and increased patient satisfaction.
When the calcar preparation is performed using a guided calcar broach, minimally invasive surgery can be performed. The disclosed broaching system is utilized for the calcar preparation in a hip prosthesis operation.
In view of the above, it would be desirable to have a calcar preparation instrument that can be utilized through a smaller incision during a surgical process.
According to one aspect of the disclosure, an apparatus is provided for creating a cavity in a bone, said cavity (i) having a cross section which has a generally triangular profile having a first side generally parallel with an axis of the bone and a second side forming an acute angle with the first side, and (ii) being contiguous with a pre-existing conical cavity in the bone. The apparatus comprises as shaft and a broach. The shaft has a longitudinal axis. The broach is mounted to the shaft and has a first cutting side mounted at the acute angle relative to the longitudinal axis of the shaft. The first cutting side is formed to include teeth. The shaft and broach are configured so that when the longitudinal axis of the shaft is advanced into the bone along the axis of the bone, the teeth of the broach form the triangular cavity.
According to a second aspect of the disclosure an apparatus for creating a cavity in a bone for receiving a prosthesis which has a conical portion and a projection of a generally triangular profile is provided. The apparatus comprises a shell, a shaft and a broach. The shell comprises a conical portion which defines a longitudinal axis and a shaft-receiving cavity for receiving a shaft. The shaft is configured to be received in the shaft-receiving cavity and be movable with respect to the shell along the longitudinal axis when so received. The shaft is configured to carry a broach having a cutting surface disposed at an acute angle relative to the longitudinal axis. The broach has a generally triangular profile and includes oppositely facing spaced apart triangular shaped side walls between which the cutting surface extends. The broach is mounted to the shaft.
According to yet another aspect of the disclosure, a method for cutting a triangular cavity in bone is provided. The method comprises a providing a shaft step, an incising step and a cutting step. The provided shaft is configured to be movable relative to the bone to be prepared and includes a broach coupled thereto to dispose a cutting surface of the broach at an acute angle relative to the shaft. The shaft and broach have a width defined by the distance between the shaft and the outer most portion of the cutting surface. The incising step includes incising the patient adjacent the bone to be prepared to form an incision having a length approximating the width of shaft and broach. The cutting step includes cutting the cavity by driving the broach by moving the shaft relative to the bone.
The disclosed broaching system is configured to reduce the size of incision required for preparation of a bone to receive a prosthetic stem therein.
The accompanying drawings, which are incorporated in and constitute part of the specification, illustrate the preferred embodiments of the invention, and together with the description, serve to explain the principles of the invention. It is to be understood, of course, that both the drawings and the description are explanatory only and are not restrictive of the invention.
Corresponding reference characters indicate corresponding parts throughout the several views. Like reference characters tend to indicate like parts throughout the several views.